Heretofore, in a fixing apparatus of electrophotographic equipment, a so-called two-roller arrangement has been employed, which essentially includes two rollers, a heating roller having a heat source built-in and a pressing roller pressed to the heating roller with a predetermined pressure. In parallel with various related patent applications, this arrangement has been widely used.
As a conventional structure of a heating roller used in the above fixing apparatus, there is generally known a so-called two-layer structure having a core, a primer layer applied on the peripheral surface of the core, and a resin layer bonded to the core through the primer layer. As a material of the resin layer, PTFE (polytetrafluoroethylene) has heretofore been applied. This PTFE resin layer is desirable in view of long life or durability because it has a sufficient hardness and an excellent scratch resistance standing for a level of wear of the layer caused by a contacting object, such as sheets and separating claws, during passing sheets therethrough.
However, the PTFE resin layer is inferior in releasing ability. Specifically, a drawback is pointed out that an unfixed toner tends to be attached onto the peripheral surface of the roller and is thus attached again onto the surface of a succeeding sheet, resulting in a problem of image. Thus, PFA (perfluoroalkoxy resin) has heretofore been developed and come into practice use as the resin layer. A heating roller having the PFA resin layer can assure to improve the releasing ability and solve the problem of image, but causes an adverse problem of an inferior scratch resistance (i.e. inferior durability).
As described above, the conventional fixing rollers, such as heating rollers, are in the situation that giving weight to releasing ability causes a deteriorated scratch resistance, while giving weight to scratch resistance causes a deteriorated releasing ability. A material capable of solving both problems all at once has not been found out.
It can be assumed to combine PFA resin with PTFE resin. However, it is difficult to arrange an adequate condition to fully bring out advantages of both resins due to different melting points between both resins. As a result, while such a material is come into practice use, it still involves some problems to be solved.